1. Field of the Invention
The invention relates to a system for utilizing the waste heat of an internal combustion engine via the Clausius-Rankine cycle process, a method for operating a system for utilizing the waste heat of an internal combustion engine via the Clausius-Rankine cycle process, and an internal combustion engine with a system for utilizing the waste heat of the internal combustion engine via the Clausius-Rankine cycle process.
2. Description of the Background Art
Internal combustion engines are used in various technical applications for converting thermal energy into mechanical energy. In motor vehicles, especially in trucks, internal combustion engines are used to move the motor vehicle. The efficiency of internal combustion engines can be increased by the use of systems for utilizing the waste heat of the internal combustion engine by means of the Clausius-Rankine cycle process. In this process, the system converts the waste heat of the internal combustion engine into mechanical energy. The system comprises a circuit having lines with a working medium, e.g., water, a pump for conveying the working medium, an evaporator heat exchanger for vaporizing the liquid working medium, an expander, a condenser for liquefying the vaporous working medium, and a collecting and equalizing tank for the liquid working medium. The overall efficiency of the internal combustion engine can be increased by the use of this type of system in an internal combustion engine, in the case of an internal combustion engine having this type of system as a component of the internal combustion engine.
In the evaporator heat exchanger, the working medium, for example, water, is vaporized by the waste heat of the internal combustion engine and then the vaporized working medium is supplied to the expander, where the gaseous working medium expands and performs mechanical work by means of the expander. In the evaporator heat exchanger, for example, the working medium is conveyed through a flow duct and exhaust gas of the internal combustion engine through an exhaust gas flow duct. As a result, the heat of the exhaust gas with a temperature in the range of, for example, between 400° and 600° C. is transferred to the working medium in the evaporator heat exchanger and, as a result, the working medium is converted from the liquid state to the vapor state.
There are two optimization criteria for the performance of the evaporator heat exchanger. On the one hand, the pressure loss should be as minimal as possible; i.e., the evaporator heat exchanger should cause as low a pressure loss as possible during the conveying of the working medium. This means that there should be if possible no deflections or internal structures to be able to provide as low a pressure loss as possible in the flow duct and a plurality of flow duct parts connected hydraulically in parallel. It should be considered in this regard that with the vaporizing of the working medium and the associated change in the physical state, the flow velocity increases greatly and thereby the pressure loss increases. A second optimization criterion is the thermal efficiency, i.e., the best possible heat transfer from the exhaust gas to the working medium. If the evaporator heat exchanger is designed, for example, as a plate heat exchanger or with a stacked plate structure, the working medium flows through a flow duct through the fluid ducts forming between the plates and the exhaust gas through the exhaust gas flow duct. In this case, a flow duct part for conveying working media and an exhaust gas flow duct as an exhaust gas flow duct part for conveying the exhaust gas form alternately on the plates, stacked one above the other, of the evaporator heater exchanger. In this case, the flow duct parts are connected in parallel; i.e., downstream of an inlet opening for the working medium in the evaporator heat exchanger, the entire working medium is first introduced into a flow duct and the working medium flows from the flow duct into a plurality of flow duct parts, connected hydraulically in parallel, and then after flowing out of the flow duct parts connected in parallel, the working medium again flows into a flow duct and from the flow duct the working medium again leaves the evaporator heat exchanger through an outlet opening.
The exhaust gas conveyed through the exhaust gas flow duct or the exhaust gas flow duct parts may have a nonuniform flow distribution; in other words, substantially less exhaust gas is conveyed per unit time in the individual exhaust gas flow duct parts than through other exhaust gas flow duct parts. This can have the result that the working medium is vaporized even earlier in individual flow duct parts, through which the working medium is conveyed, than in other flow duct parts. The earlier vaporizing of the working medium and the associated change in the physical state from liquid to gaseous lead to an intensification of the effect of unequal distribution, because the pressure loss also increases with the change in the physical state due to the higher flow velocity of the working medium and this results in an additional reduction in volume flow in the flow duct parts with an earlier vaporization. This can have the result that because of the high volume flow in the flow duct parts with a later vaporization, the working medium leaves the flow duct part in a liquid state and in other flow duct parts the working medium leaves the flow duct part as a gas. As a result, a mixture of liquid and gaseous working medium can emerge at the outlet opening of the evaporator heat exchanger; this is disadvantageous for the overall coverage of the system and in particular can also cause damage in the expander.
WO 2009/089885 A1 shows a device for exchanging heat between a first and a second medium, with plate pairs stacked one on top of another in a stacking direction, whereby a first flow space, through which a first medium can flow, is formed between the two plates of at least one plate pair and a second flow space, through which a second medium can flow, between two plate pairs, adjacent to one another, whereby the first flow space has a first flow path for the first medium with flow path sections which can be flown through one after the other in opposite directions, said sections being separated from one another by a partition wall arranged between the at least two plates of the at least one plate pair.